Designed for small businesses, IPCop lets you turn an old PC into a network appliance that protects against threats and speeds Web access. It's easy to use, and it works with just about every type of connection from dial-up to leased lines. Operating System: Linux.

Like IPCop, Endian Firewall Community contains a complete Linux distribution that can be used to turn any PC into a firewall appliance. It includes antivirus, anti-spam, Web content filtering, and VPN capabilities. Operating System: Linux.

Like many of the other apps in this category, Devil-Linux was originally intended to be used to turn an old PC into a firewall/router. Now the program has been updated so that it can also be used as an application server. Operating System: Linux.

Turtle Firewall is fast and easy-to-use--if you know what you're doing. You define and select which zones, hosts, networks, and services you want to enable, which gives you a lot of control but requires a good understanding of network security. Operating System: Linux.

Shorewall (aka "Shoreline Firewall") makes it easy to configure Netfilter so that it can be used as a firewall on a standalone system or as part of a gateway appliance on a network. Once installed, it can also be used to monitor Netfileter actions. Operating System: Linux.

Like Shorewall, FireHOL isn't an actual firewall as much as a firewall configurator. It aims to make understanding and configuring firewalls easy, even for those with limited knowledge on the subject. Operating System: Linux.

Sentry combines firewall, server, and intrusion detection capabilities onto a bootable CD. It relies on a number of well-known open source apps, including Open VPN, Snort IDS, NMap, and more. Operating System: Linux.

Designed to be easy to use, Vuurmuur is an iptables-based firewall that doesn't require any knowledge of iptables. It offers real-time log and connection viewing, filtering, traffic volume accounting, auditing, and more. Operating System: Linux.

Short for "Open Digital Evidence Search and Seizure Architecture," ODESSA contains a number of different tools for collecting and analyzing digital evidence. With more than seven years of development behind it, the project is fairly mature, and the site contains links to a number of other forensics-related projects. Operating System: Windows, Linux, OS X.

Live View creates a virtual machine from a raw disk image or physical disk. As a result, you can see and interact with a PC just as the user did, without changing the environment or endangering your own PC. Operating System: Windows.

Calling itself "an opensource watchdog for Windows," Winpooch incorporates anti-spyware and anti-trojan capabilities with ClamWin Antivirus. It aims to give the user complete control over which programs are running on the system. Operating System: Windows.

The DemocraKey tagline says it all: "It's like a condom for your computer." Install it on a portable drive and plug it in to any computer. DemocraKey scans for viruses and protects your privacy while you surf. Operating System: Windows.

Short for "Another File Integrity Checker," AFICK monitors changes to your file systems in order to alert you to possible intrusion. If you're familiar with Tripwire, AFICK will look and feel very familiar. Operating System: Windows, Linux, Unix.